System for automatic control of electron beam heating device

ABSTRACT

A system is disclosed for automatic control of an electron beam heating device of the type in which a current-stablized powersupply source is coupled to the electron gun and is electrically connected with an automatic reset unit serving to cut off voltage to the electron gun upon an electric breakdown between the electrodes of the gun. The automatic reset system does not operate immediately following the breakdown between the electrodes of the gun, but only after a predetermined time interval to allow the voltage across the electron gun to return spontaneously to the original value when the discharge between the electrodes of the electron gun is unsteady in character. After voltage cut off, if the electrical breakdown still has not been corrected, the automatic reset system successively operates at different time intervals to cut off electron gun voltage. Specifically, and in the preferred embodiment, the instant inventive system is so designed that the time interval between the occurrence of voltage cut off as a result of electric breakdown and the occurrence of the subsequent automatic reset of the apparatus becomes increasingly larger during successive operation of the system.

Kiln-1Z1 ELECTRON BEAM HEATING DEVICE Primary Examiner-J. V. TruheAssistant Examiner-G. R. Peterson v [76] In enters i gg fir gyfy iigtgsgAttorney, Agent, or Firm-Holman & Stern 2-B, kv. l6; Pavel BorisovichYakolvlev, ulitsa Tolvukhina, 9, [57] ABSTRACT 5:32; g TJ E 5:53:21??? Asystem is disclosed for automatic control of an elecumsa 29 kv. 8 a of M08 c ow tron beam heatmg dev1ce of the type in wh1ch a cur- U Srent-stabhzed power-supply source 1s coupled to the electron gun and iselectrically connected with an au- [22] Filed: Aug. 11, 1971 tomaticreset unit serving to cut off voltage to the electron gun upon anelectric breakdown between the [21] Appl' 170915 electrodes of the gun.The automatic reset system Related US. Application Data does not operateimmediately following the break- [63] Continuation-impart of Ser. No.80,235, Oct. 12, down between the electrodes of the g but y after 1970,abandoned, which isacontinuation of Ser. No. a p edete i time intervalto allow the voltage 836,449, June 25, 1969, abandoned. across theelectron gun to return spontaneously to the original value when thedischarge between the elec- [52] US. Cl. 219/121 EB, 315/119 trodes ofthe electron gun is unsteady in character. [51] Int. Cl B231 15/00 Aftervoltage cut off, if the electrical breakdown still [58] Field ofSearch... 219/121 EB, 121 EM, 69 P, has not been corrected, theautomatic reset system 219/69 C; 315/119, 127, 107; 317/141, 157successively operates at different time intervals to cut off electrongun voltage. Specifically, and in the pre- [56] References Cited ferredembodiment, the instant inventive system is so UNITED STATES PATENTSdesigned that the time interval between the occur-- 2 619 52s 11/1952Webb .Q 315/127 x rence of voltage cut off as a result of electric311931722 7/1965 Opitz 315 30 and the currence of the subsequentautomatlc 3,196,246 7/1965 219/69 reset of the apparatus becomesincreasingly larger 3,20 ,33 10 19 5 143 5 during successive operationof the system. 3,459,941 8/1969 315/107 X 3,483,347 12/1969 Losey 219/69P 3 Clalms, 4 Drawlng Flglll'es H POWER SUPPLY f z T BLOCK POWER BLOCKAUTOMATlC SUPPLY CONTROL REPEATED SWITCHING 3 J 4 J DESIGN United StatesPatent [1 1 Brukovsky et al.

[111 3,826,889 [451 July'30, 1974 SYSTEM FOR AUTOMATIC CONTROL OFPATENTfiijJULS 0 2914 saw 1 er 2 POWER SUPPLY ELECTRON HEATING DESIGNBLOCK AUTOMATIC REPEATED SWITCHING BLOCK POWER SUPPLY CONTROL FIG. 1

U VO LTAGE TIME POWER SUPPY 1 INVENTOR I ELECTRON HEATING DESIGN FIG. 3

ATTORNEY PATBIIEINIIIB A 3.826.889

sIIE 2 IF2 ll. 3 1 I 22 1F HAND. SWITCHING 56 67 74 R T S l W4 AUTOMATIC24 I7 REPEATED S S -L- sw TC H IN G ARs l T 8 2PB BLOCKING UNDER Ia) 2 9I. OPENED LINE CONTACTOR 32 I (RK) Q I {34 43 STEADY DISCHARGE 212.DIsCERNING IQ4O 4| CONTAC S .MULTI PLYING 3 Q RELAY 5 44 I 1T" ARSOPERATED CIRCUIT i5 58 EBLOC KING F ID I CONTACTS MuLTIPLY NG Q 47 57 TME DELAY BEFORE THE 1|' |F* FIRST REPEATED 36 59 Q 64 sw TCH NG TIMDELAY BEFORE THE Q62 5| SECOND REPEATED ll 63 SWITCHING -(NB) 37 3 gTIME DELAY BEFORE THE I IT I THIR REPEATED 8 SWITCHING C69 52 8 S70 ARsOPENING II H A C38 71 72 -1 k INVENTOR F1614 BYM4-V m4 ATTORNEY SYSTEMFOR AUTOMATIC CONTROL OF ELECTRON BEAM HEATING DEVICE This applicationis a Continuation-ln-Part of copending application Ser. No. 80,235 filedOct. 12, 1970 now abandoned, which application, in turn, is acontinuation of application Ser. No. 836,449, filed June 25, l969 nowabandoned.

This invention generally relates to the field of electrothermics andmore particularly concerns systems serving to automatically controlelectron beam heating devices.

As is generally known, electric heating devices having electron guns aresupplied from special power sources which comprise commutation meanssuch as a contactor or high-voltage switch to connect the supply sourceto and disconnect it from the supply network at the end of an operatingprocess or in emergency situations, a step-up transformer and arectifier comprising controllable or uncontrollable valves or switchesand having its negative terminal connected to the cathode of theelectron gun, while its positive terminal is connnected to the anode ofthe electron gun. Such supply sources for use with electron beam heatingdevices essentially are of two types.

One such supply source ensures a constant voltage value at the output ofthe rectifier supplying the electron gun with the voltage value beingindependent of the conductance of the electron gun. When electricalbreakdown occurs between the anode and the cathode of the electron gunin an electric heating device supplied from a source of this type, as isfrequently the case with industrial apparatus, the conductance of theelectron gun sharply rises with the result that a current exceeding manytimes the rated value flows through the supply transformer, therectifier and the electron gun. An arc discharge sparks between thecathode and the anode of the electron gun which is likely to melt andput the electrodes of the electron gun out of action.

This mode of operation occurs in emergencies, requiring immediatedisconnection of the electron gun by either disconnecting the supplysource of the heating device from the network with the help of thecommutation means incorporated in the supply source, or by suitablyrendering inconductive the valves of the rectifier supplying theelectron gun. Subsequently, some time after the disconnection of supplyfrom the electron gun, the electric strength and, consequently, theconductance of the electron gun are restored to the original level dueto the recombination of plasma that has formed during the burning of theelectric are between the anode and the cathode. To continue theoperational process, voltage then is re-applied to the electron guneither manually by the operator or by an automatic reset system througha control unit of the supply source commutation means or the controlunit of the rectifier valves.

In cases when the time interval between the cutoff of supply from theelectron gun and voltage re-supply by the automatic reset system isinsufficient to restore the electrical strength of the interelectrodegap, resetting may result in another breakdown between the anode and thecathode of the electron gun and require a further disconnection ofsupply from the electron gun to eliminate the emergency operation.Commonly known automatic reset systems for use with electron beamdevices supplied from sources maintaining a constant voltage value atthe rectifier are characterized by instantaneous (no time delay)disconnection of the supply from the electron gun upon electricalbreakdown between the electrodes thereof, and by identical timeintervals between each successive reset operation.

A further basic type of supply source serves to maintain a constantcurrent value at the output of the rectifier supplying the electron gun,the current value being independent of the conductance of the electrongun. Supply sources of this type are generally constructed utilizingvarious resonance circuits, i.e., Boucherot Steinmitz circuits orvariants thereof, or utilizing a controlled rectifier which supplies theelectron gun to ensure l const. In electron beam heating devicessupplied from sources of this type, when electrical breakdown occursbetween the cathode and the anode of the electron gun and an electricdischarge sparks between them, the current does not change in thecircuit formed by the supply transformer, the rectifier and the electrongun. The voltage at the electron gun, however, drops to a valuedetermined by the parameters of the discharge sparking between the anodeand the cathode of the electron gun. This electric discharge subsists onthe vapors of metal evaporating from the electrodes of the electron gunand on gases dissolved in metals, and it is characterized by low powerevolving in the electrodes. For this reason, it can either be steady orunsteady, i.e., last as long as voltage is applied to the electron gun,or spontaneously die out after a certain time interval. In the lattercase, the conductance of the electron gun decreases and the voltageacross it rises to the value existing before the breakdown.

The character of this discharge, i.e., steady or unsteady, depends onmany factors, the most important of which are the material from whichthe electrodes of the electron gun are made, the value of the dischargecurrent, the extent of vacuum in the interelectrode gap, the relationbetween the amount of vapors and gases formed during the discharge andthe speed vapors and gases formed during the discharge and the speedwith which they are discharged from the interelectrode gap. When thedischarge is unsteady it is not advisable to cut off supply from theelectron gun in an attempt to eliminate the breakdown. But when thedischarge is steady, it can be eliminated by disconnecting the supplyfrom the electron gun through the commutation means of the supply sourceor through the controllable valves of the rectifier connected to theelectron gun.

Thereafter, to continue the normal operating process, voltage should notbe applied to the electron gun immediately after it has been cut off,but only after a definite time interval which must be sufficient forionization to take place in the interelectrode gap of the electron gun.If during this time interval the electrical strength of theinterelectrode gap has not returned to its normal value, re-applyingvoltage to the electron gun will result in another breakdown between thegun electrodes.

The instant invention has, as a primary object thereof, the provision ofan automatic control device for electron beam heating apparatus suppliedfrom current-stabilized power sources of the type abovedescribed, theautomatic control device of the instant invention ensuring automaticrestarting of the electron beam heating apparatus after the power supplyhas been cut off from the electron gun due to an electric breakdownbetween the electrodes thereof.

A further object of the instant invention concerns the provision of anautomatic reset system which will cut off voltage from the electron gun,not immediately following the electric breakdown between the electrodesof the gun, but only after a predetermined time interval. This timeinterval between breakdown in the electron gun and cut off of the powersupply is intended to allow the voltage across the electron gun tospontaneously return to the original value without a forceddisconnection of supply when the discharge between the electrodes of theelectron gun is unsteady in character, the automatic reset system beingeffectively utilized only with electron guns supplied fromcurrentstabilized sources.

A further object of the instant invention concerns the provision of anautomatic reset system which, upon the presence of recurring electricbreakdowns between the electrodes of an electron beam heating apparatus,serves to successively reset the system and re-apply voltage to theelectrodes with different time intervals between the successive resets,the duration of each time interval being varied at will. In thisrespect, the system of the instant invention is contemplated to functionsuch that the time interval between the initial cut off of voltage as aresult of the first breakdown and the subsequent automatic reset of theelectron beam heating apparatus is smaller than the interval between thecut off occurring as a result of a second breakdown and the subsequentautomatic reset of the apparatus, and so on.

A still further object of the instant invention concerns the provisionof a system of the type described wherein the overall efficiency andcapacity of the electron beam heating device is increased and whereinthe life of the switching equipment such as a contactor, an automaticswitch or a high-voltage switch incorporated in the supply source of theelectron beam heating apparatus and serving to connect and disconnectthe supply source to the network, is markedly prolonged. Through theutilization of the automatically reset unit of the instant invention thenumber of cut outs of the powersupply source is reduced.

These objects as well as others which will become apparent as thedescription proceeds, are implemented by the instant invention which, asaforestated, comprises a system for the automatic control of an electronbeam heating device, the system broadly comprising a powersupply sourceelectrically connected with an automatic reset unit in which, inaccordance with the invention, the power-supply source is constructed inthe form of a current-stabilized power source. The automatic reset unitof the instant invention is provided with a plurality of time delayelements as will be discussed hereinbelow to ensure prescribed timeintervals between the occurrence of short circuits at the interelectrodegap between the electrodes of the electron gun, and subsequent cut offoperations of the power-supply in an effort to correct the electricbreakdown between the electrodes.

The various advantages of such a system wherein operation of theautomatic reset unit occurs only during prescribed and variable timeintervals as abovediscussed can perhaps best be understood from thefollowing general discussion.

In this respect, it should be recognized that a chief cause of a shortcircuit of the electron gun or interelectrode load in an electron gunelectric heating device may be an electric breakdown between theelectrodes of the electron gun. It the power-supply source is of thetype which provides a constant value of supply voltage, such aninterelectrode breakdown leads to a heavy current arc discharge.

After breakdown, the time of recovery of the electric strength of thegun to the rated value depends, as briefly discussed above, on therelationship between the amount of vapours and dissolved-in-metal gasesentering the interelectrode gap between the electrodes of the electrongun from the working chamber of the device and evolving from thematerial of the electrodes during the arcing and the efficiency of thevacuum chamber of the electron gun. During the process of melting, therecovery time may change.

If the power-supply source for the electron gun is based on a systemproviding a constant value of interelectrode current, the currentflowing through the power-supply circuit of the device would remainunchanged upon a short circuit between the electrodes. Therefore, theshort circuit conditions characterized by a considerable voltage drop atthe output of the powersupply source are not emergency conditions whichwould require an immediate cut off of the device, even though such shortcircuit conditions do interupt the normal course of the particulartechnological process being undertaken. This is clear from the followingconsideration.

During a breakdown of the interelectrode gap, an arc discharge appearsbetween the electrodes of the gun, which discharge is characterized byan insignificant power of the arc. In this event, the power dissipatedin the electrodes is not high and, as is found from experience, suchdissipated power does not cause notable destruction of the electrodes.Such destruction of the electrodes, i.e., melting or erosion of thematerial of the electrodes, is a heavy-current discharge sparking tookplace between the anode and cathode of the electron gun. In the case ofa weak-current discharge of the type now under consideration lastingonly for a relatively short time, such destruction is substantiallyabsent.

Furthermore, the stability of the discharge burning, whether thedischarge be steady or unsteady, is determined by the relationshipbetween the amount of vapours and dissolved-in-metal gases admitted intothe interelectrode gap from the working chamber of the device and alsoevolved from the material of the electrodes and the efficiency of thevacuum system of the electron gun.

In some cases when the arc discharge is unstable, the normal operatingduty of the electron gun device is automatically restored after acertain time interval. In such cases, the application of presently knownapparatus which serve to cut off the power-supply source immediatelyafter receiving a signal from its output would lead to unjustifieddisconnections of the device from the power-supply source and thus to aresultant decrease in the device efficiency and to deterioration of theswitching equipment utilized therein.

The utilization of the present inventive system, on the other hand,avoids these disadvantages due to the time delay occurring before thefirst cut off upon detection of an electric breakdown between theelectrodes, and through the provision of variable time delays betweensubsequent reset operations in the event that the electric breakdownbetween the electron gun electrodes persists.

The present inventive system is thus designed to ensure automaticcontrol of the electron beam heating apparatus and, for this purpose,the instant invention will be seen to utilize a signal which isproportional to the output voltage of the apparatus supply source, whichsignal is applied to the input of an automatic reset unit. The automaticreset unit itself will be seen to comprise several relays which ensuresthe required succession of logical operations, the reset unit furtherincluding time relays for maintaining preset time intervals betweenoperations. The output of the automatic reset unit of the instantinvention is connected to the input of the control unit of the electrongun powersupply source. As the power-supply is automatically cut off bythe automatic reset system, the signal from the output of the automaticreset unit is applied to the input of the control unit of thepower-supply source so as to influence the operation of the power-supplysource in one of two manners depending on the particular design of thesupply source for the electron beam heating apparatus.

Specifically, if the rectifier utilized in the powersupply source isconstructed of uncontrolled valves, the control unit of the power-supplysource would generate a signal to cut off the supply source from thenetwork through the commutation means such as a contactor orhigh-voltage switch incorporated in the supply source. Alternatively, ifthe rectifier of the power-supply source is constructed utilizingcontrolled valves, the control unit of the supply source would generatea signal to the valves such that the valves would assume anon-conductive state.

The invention itself as well as further operational advantages anddetails thereof will become apparent from the following description of apreferred inventive embodiment, such description referring to theappended sheets of drawings wherein:

FIG. 1 depicts a block diagram of the novel system of the instantinvention serving to automatically control an electron beam heatingdevice;

FIG. 2 depicts a time diagram of the operation of the automatic resetsystem;

FlG. 3 is a schematic diagram of a supply circuit for the electron gunapparatus, the supply circuit comprising a parametric power-supplysource serving to maintain an invariable value of current flowingthrough the supply transformer, and a power rectifier utilizinguncontrolled valves; and

FIG. 4 depicts a schematic diagram of the control unit of thepower-supply source, and of the automatic reset unit of the instantinvention in an embodiment thereof utilizing contact relays for tripleautomatic reset cycling as will be explained hereinbelow.

Referring now to the drawings, the overall structure and operation ofthe novel invention will be discussed and, as is seen from FIG. 1 of thedrawings, an electron beam heating device 1 is fed from acurrrent-stabilized power-supply source 2 which, in turn, is connectedwith a unit 3 for controlling the power-supply source 2.

The output of the power-supply source 2 of the device is electricallyconnected with an automatic reset unit 4 constructed in accordance withthe teachings of the instant invention and provided with a plurality oftime delay elements such as relays of both the single contact andmultiple contact and independently operated variety as will be discussedin more detail hereinbelow. The automatic reset unit 4 is connected withthe power-supply source unit 3 so as to operate same to effect cut offof power to the electron beam device in a predetermined manner.

The proposed system operates as follows. If the breakdown in theelectron gun of the device 1 occurs at a time moment t (FlG. 2), the useof the time delay element makes it possible to cut off thecurrentstabilized power-supply source after a definite time interval A Ii.e., in the case of appearance of a comparatively stable short circuit.

The first automatic reset of the device I will take place after a timeinterval At If during the time interval Ar or to the time moment t;, theelectric strength of the device 1 is not restored to the rated value,the device 1 will be cut off again within the time interval t The secondautomatic reset of the device will take place only after a time intervalAL If during this time or during the time M the electric strength of thedevice 1 does not reach a corresponding level, the device 1 will beswitched off at the moment 1 and will be switched on again only afterthe time interval At If the electric strength of the interelectrode gapdoes not come up to its rated value for the time Ar or M the device willagain be switched off within the time period t,,. The automatic resetunit 4 is switched off simultaneously with the device. The subsequentreset of the device 1 can be carried out only by hand.

Thus, the proposed system features a limited number of reset cycles thequantity of which may be determined on the basis of the experience ofoperation of the device.

If during the time period An; after the first reset or during the periodAt after the second reset the breakdowns in the device do not occur, theautomatic reset unit 4 with the help of the time delay element is set tothe initial position corresponding to the time period t The proposeddevice provides for the possibility of individual adjustment of the timeintervals Al At A2 At and At whose optimum values are selectedexperirnentally.

It should be noted that the selection of the time intervals At At, Atensures a higher stability of operation of the device because therepeated cut off of the device, for example during the time period An,proves that the time interval A1 was insufficient for restoring theelectric strength of the device up to the rated value.

The various time intervals At generally are selected to have unitsranging from a few hundreths of a second to a few seconds, thedifferences in the selected units being dependent on the specifics ofthe operating process carried out in the apparatus and of the parametersand design of the automatic reset system itself.

With the above general operation and structure in mind, the followingdetailed description of an actual physical embodiment of the inventioncan be better understood. In this respect, and referring specifically toFIG. 3 of the drawings, the electron beam heating apparatus 1 comprisesan electron gun 200 have a cathode 300 and a focusing anode 400. Anelectron beam 5 shaped in the interelectrode gap 6 passes through anorifice in the focusing anode electrode 400 to the article 7 to beheated which, like the focusing anode electrode 400, is held at groundpotential. The filament cathode 300 is fed from a supply transformer 8.

A supply source 9 of the electron beam heating apparatus comprisescommutation means such as a contactor, whose power contacts 10 areconnected in series to a supply transformer 11 and reactive elements bycapacitor 12 and inductor l3, and also a rectifier 14 connected to thesupply transformer 11 and having its negative terminal connected to thecathode 300 of the electron gun, while the positive terminal isconnected to the article 7 to be heated. When the reactances of thecapacitor 12 and the inductor 13 are equal, the circuit formed by theelements 11, 12 and 13 ensures a constant value of current flowingthrough the primary winding of the transformer 11 irrespective of theconductance of the electron gun 200 and, with a sufficiently hightemperature at the electron gun cathode, this ensures a constant valueof current in the electron beam 5.

An additional resistor 15 is provided to allow control of the supplysource voltage which may vary with changes in the conductance of theelectron gun. One terminal of the additional resistor 15 is connected tothe negative terminal of the rectifier l4 and the other, to the coil ofa voltage relay 16, whose second terminal is connected to the positiveterminal of the rectifier 14. The power contacts 10 of the commutationmeans of the supply source 9 are controlled by means of the coil of acontactor 17.

Referring to FIG. 4, the control unit of the supply source comprises onon-button 18, on off-button 19,

coils of intermediate relays and 21 and the coil of the contactor 17.When the button 18 is pressed, the coil of the relay 20 is energized andone of its contacts 22 interlocks the button 18 while the other contact23 supplies the coil of the relay 21. As the latter operates, itscontacts 24 and 25 directs supply to the coil of the contactor l7 and,at the same time, the contact 26 feeds supply to the coil of the timerelay 27 whose contact 28, having a time delay upon closure, preparesthe supply circuit of the coil of a time relay 29 for operation. Sincethe contact 28 closes with a time delay, the time relay 27 interlocksthe operation of the relay 29 in case the coil of the contactor 17 isde-energized.

When the supply voltage of the electron gun decreases, the coil of thevoltage relay 16 releases and the relay closes its contact 30 in thecircuit of the coil of the time relay 29 which is capable ofdistinguishing whether the discharge between the electron gun electrodesis steady or not, ensuring a time delay At in accordance with FIG. 2.

If the discharge between the electron gun electrodes and the voltagedrop caused by it in the supply source last longer than the time presetin the time relay 29, the latter opens one of its contacts 31, cuttingoff supply of the coil of the relay 21 with the result that the coil ofthe contactor 17 is deenergized, while its second contact 32 is closedin the circuit of the coil of the in-v termediate relay 33 serving tomultiply contacts. As the relay 33 operates, its contacts 34, 35, 36, 37and 38 close.

Upon the closure of the contact 34, voltage is applied to the coil of anintermediate relay 39 which operates and causes one of its contacts 40to block supply through the contact 34, while the other contact 41directs supply to the coil of a time relay 42 which unlocks theautomatic reset circuits that have operated. If no recurrent breakdownstook place in the electron gun for the time period At, in accordancewith FIG. 2, the

relay 42 opens its contacts 43 and 44 and returns the automatic resetsystem to the condition corresponding to the time t of the diagram inFIG. 2.

When the relay 20 operates, its third contact 45 directs supply to thecoil of the intermediate relay 46 serving to multiply contacts. Uponoperation, the relay 46 closes its contacts 47, 48 and 49, preparing tolock the supply circuits of the coils of the time relays 50, 51, and 52which ensure time delays Atg, At, and At in accordance with the diagramin FIG. 2.

When the relay 33 operates, its contact 35 directs supply to the coil ofan intermediate relay 53 which, upon operation, causes one of itscontacts 54 to block supply through the contact 35, while the othercontact 55 directs supply to the coil of the time relay 50.Simultaneously the relay 53 opens its contact 56 in the circuit of thecoil of the relay 21 with the result that the coil of the contactor 17is de-energized and the supply source of the electron gun is cut offfrom the network.

After a time interval At in accordance with FIG. 2, the time relaycloses one of its contacts 57, blocking supply of its coil through thecontact and opens its contact 58 in the circuit of the coil of the relay53. The coil of the relay 53 is de-energized, its contact 56 closes andthe coil of the relay 21 is again energized, resulting in the firstautomatic reset of the coil of the contactor 17.

Simultaneously, the third contact 59 of the relay 50 prepares the supplycircuit of the coil of the intermediate relay 60 for operation.

If, by a definite time, the discharge between the electrodes of theelectron gun has not stopped spontaneously, at that moment the relay 29operates again, its

contact 31 cutting off supply from the coil of the relay 21 so that thecontactor 17 is cut off. At the same time the contact 32 of the relay 29directs supply to the coil of the relay 33 which, upon operation, causesits contact 36 to direct supply to the coil of the intermedi ate relay60.

As the relay 60 operates, one of its contacts 61 blocks supply of thecoil through the contact 36, while the other contact 62 directs supplyto the coil of the time relay 51 which maintains a time delay At, inaccordance with FIG. 2. At the time t the relay 51 operates and, withthe help of the contact 63, blocks supply of its coil through thecontact 62. When the relay 51 operates, it closes its contact 65 in thecircuit of the coil of an intermediate relay 66 and opens its contact 64in the circuit of the coil of the relay 60. As a result, the contact 67of the relay 60 closes, directing voltage to the coil of the relay 21,thereby effecting a second automatic reset of the contactor 17 at thetime time If by the time the discharge between the electron gunelectrodes has not stopped spontaneously at that moment the relay 29operates again, its contact 31 cutting off supply from the coil of therelay 21 after the time interval Al with the result that the contactor17 is cut off. Simultaneously, the contact 32 of the relay 29 directssupply to the coil of the relay 33 which, upon operation, causes itscontact 37 to direct supply to the coil of the intermediate relay 66.

As the relay 66 operates, its contact 68 blocks supply of the coilthrough the contact 37, while its other contact 69 directs supply to thecoil of the time relay 52 which effects a time delay At, in accordancewith FIG. 2.

At the moment t,, the relay 52 operates and with the help of a contact70, blocks supply of its coil through the contact 69. Upon operation,the relay 52 closes its contact 71 in the circuit of the coil of anintermediate relay 72 and opens its contact 73 in the circuit of thecoil of the relay 66. As a result, the contact 74 of the relay 66closes, directing supply to the coil of the relay 21, thereby effectinga third automatic reset of the contactor 17 at the time 1 If by the timet, the discharge between the electron gun electrodes has not stoppedspontaneously, at that moment the relay 29 operates again, its contact31 cutting off supply of the coil of the relay 21 after a time intervalAt, with the result that the contactor 17 is cut off. At the same time,the contact 38 of the relay 29 directs supply to the coil of anintermediate relay 72 which, upon operation, opens its contact 73 in thecircuit of the coil of the relay 20, disconnecting the automatic resetsystem.

The contactor 17 may again be energized manually be means of the button18.

Due to the different operation time of the relays 50, 51 and 52, thepresent system maintains different time intervals At AL, and At betweenthe disconnection of the supply source from the network and itssubsequent automatic resetting.

As should now be apparent, the objects initially set forth at the outsetto this specification have been successfully achieved.

What is claimed is:

1. A power supply system for an electron beam heating device havingelectrodes, said system comprising, in

combination: a current-stabilized power-supply means for providing saidelectron beam heating device with a substantially constant current; acontrollable switching means for selectively disconnecting andreconnecting said power-supply means; sensing means for sensing theoutput voltage of said power-supply means and for thereby detecting theoccurrence of a short circuit between said electrodes; and an automaticreset control unit means responsive to said sensing means forcontrolling said controllable switching means, said reset unit includingtime delay logic circuit means responsive to the occurrence of a shortcircuit between said electrodes for (a) disconnecting said power supplymeans, (b) reconnecting said power supply means after a definite timeinterval, and (c) alternately disconnecting and reconnecting said powersupply means in succession if the short circuit between said electrodeshas not stopped simultaneously, said time delay logic circuit meansautomatically effecting each successive disconnect and reconnectoperation after predetermined and successively different time intervals.

2. A power supply system as defined in claim 1, wherein said time delaylogic circuit means comprises a plurality of relays disposed in a logictree arrangement, said relays having independently adjustable operationtimes.

3. A system as defined in claim 1, wherein each successive time delayperiod automatically effected by said time delay logic circuit means isrespectively longer in duration.

1. A power supply system for an electron beam heating device havingelectrodes, said system comprising, in combination: a current-stabilizedpower-supply means for providing said electron beam heating device witha substantially constant current; a controllable switching means forselectively disconnecting and reconnecting said power-supply means;sensing means for sensing the output voltage of said power-supply meansand for thereby detecting the occurrence of a short circuit between saidelectrodes; and an automatic reset control unit means responsive to saidsensing means for controlling said controllable switching means, saidreset unit including time delay logic circuit means responsive to theoccurrence of a short circuit between said electrodes for (a)disconnecting said power supply means, (b) reconnecting said powersupply means after a definite time interval, and (c) alternatelydisconnecting and reconnecting said power supply means in succession ifthe short circuit between said electrodes has not stoppedsimultaneously, said time delay logic circuit means automaticallyeffecting each successive disconnect and reconnect operation afterpredetermined and successively different time intervals.
 2. A powersupply system as defined in claim 1, wherein said time delay logiccircuit means comprises a plurality of relays disposed in a logic treearrangement, said relays having independently adjustable operationtimes.
 3. A system as defined in claim 1, wherein each successive timedelay period automatically effected by said time delay logic circuitmeans is respectively longer in duration.